illustration (attribution, if any possible, is at the end of the article)
As presented yesterday (gplus.wallez.name/LcMPKb2rLSW), the five aggregates are useful to introduce selflessness, and is a core teaching in Theravāda.
A fundamental teaching of Mahāyāna schools is buddha-nature, and it is a legitimate question to wonder how the two teachings relate.
« We all have Buddha-nature » is a core later teaching, but it is as easily mis-interpreted as the five aggregates are. This definitely does not mean we are enlightened already! This does not mean we have intrinsic "seeds of enlightenment" in us, that will mature in due time. This does not mean we're one, nor connected to Brahma…
Buddha-nature states that nothing 'in'/'of' you prevents you from becoming a buddha here&now… There is no intrinsic, unconditioned barrier between you and buddhahood.
Buddha-nature relates to the famous teachings on 'emptiness' (śūnyatā). Emptiness refers to emptiness of essence, not of existence: it accepts that phenomena exist within contexts, but it rejects that phenomena may be defined 'intrinsically', i.e. in isolation from the context in which they arise (and thus endowed with absolutes and permanency and certainties…).
The emptiness of the aggregates refers to what's usually called 'selflessness'. While Mahāyāna schools and Theravāda might disagree about the emptiness of other phenomena, they do agree about the aggregates being empty of essence.
Buddha-nature insists that the separation itself, between 'you' (empty of essence) and buddhahood, is empty of essence.
In terms of aggregates
Another way to present buddha-nature is to state that the skandhas (aggregates) are not the reason 'why' you're not a buddha just yet!
Buddha-nature does not say that the skandhas being misappropriated as a 'self' (due to 'ignorance') are not currently separating you from embodying wisdom… But buddha-nature states that nothing 'in' the skandhas forces you to appropriate them ignorantly! You 'can' stop ignorance here&now, nothing forces you to cling!
What buddha-nature states is the entity-less nature of the separation: what distinguishes you from a buddha is conditioned, impermanent, entity-less. Cease ignorance, lust and aversion and you 'are' a buddha. Don't cease (or start again after ceasing), and you 'are' not. Cease again and your 'are' again.
As it is classic in Buddhism, if you change the causes, you'll change the consequences: if you change the causes of the separation between you and buddhahood (notably 'ignorance'), the separation will fall away.
A bit more advanced:
Buddha-nature is the nature of the aggregates!
The aggregates are empty of essence, buddha-nature is emptiness of essence of a separation between you and emptiness of essence… in short, Buddha-nature is the nature of the aggregates!
And you will perceive your buddha-nature the exact moment when you'll see the aggregates as they are: empty of essence, selfless! Conversely, you do not see your buddha-nature as long as you delude yourself and see the aggregates as a 'self'.
Buddha-nature cannot be isolated, pinpointed, nor found… it lies in the possibility of responding appropriately or wisely to whatever arises here&now (without ignorance, lust or aversion biasing the response). Such a 'possibility' is ceaselessly available ('deathless') but also never predefined ('unborn'), it is 'unconditioned' nibbāna.
The aggregates 'have' buddha-nature in the same way they 'have' impermanent nature, conditioned nature, and the nature of constituting a basis for dukkha (suffering) when misappropriated… It obviously is not an inherent, intrinsic, reified 'nature'.